The two recorders, key to helping determine what happened to the plane, which plunged into the ocean May 31, will only continue to emit signals for another eight days or so.
French vessels in the search area have picked up noises regularly, but subsequent investigation has revealed no link to the black boxes, French military spokesman Christophe Prazuck told Associated Press Television News.
"The black boxes have not been found. The black boxes have not been located. We're still looking for the black boxes," Prazuck said in English.
"Regularly they have alerts. They hear noises that could be related to the black boxes so they have to investigate these noises," he added, saying the French authorities "never" have had confirmation that any of the sounds detected were related to the black boxes.
The Airbus A330 plane came down in the Atlantic after running into thunderstorms en route from Rio de Janeiro to Paris. All 228 people aboard were killed. The cause of the crash remains unclear.
The French air accident investigation agency, BEA, said in a statement Tuesday that "no signals transmitted by the flight recorders' locator beacons have been validated up to now."
The BEA said work is continuing "aimed at eliminating any doubts related to any sounds that may be heard, and any findings will be made public."
Last week, BEA director Paul-Louis Arslanian sternly warned against any unconfirmed leaks in the investigation, saying they could mislead the public and unnecessarily worry or encourage the families.
Le Monde said a mini research submarine, the Nautile, dived Monday to search for the boxes based on a "very weak signal" from the flight recorders picked up by the French ships.
Searchers from Brazil, France, the United States and other countries are methodically scanning the Atlantic for signs of the plane.
French-chartered ships are trolling a search area with a radius of 50 miles (80 kilometers), pulling U.S. Navy underwater listening devices attached to 19,700 feet (6,000 meters) of cable. A French submarine is also searching.
The black boxes send out an electronic tapping sound that can be heard up to 1.25 miles (2 kilometers) away.
Ten of 50 bodies recovered from the Air France flight have been identified as those of Brazilians, medical examiners said.
Dental records, fingerprints and DNA samples were used to identify the bodies. Investigators are reviewing all remains, debris and baggage at a base set up in Recife, Brazil.
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